What is the forum experience with tube phono preamps? Do you think is better alpha EF or NR?
I owned four ARC phono preamps (PH7, Ref 2, Ref2SE, Ref 10 Phono). The stock power cords are quite good actually. If your unit is new to you, perhaps use it for a while before changing the cord. I also used Shunyata power cords and interconnects with all of those, and each responded to the benefits the cords and wires provided. You won't make a mistake with whatever Shunyata power cord you choose.
When I reviewed the PH7 in 2006 (here
) that was with a Shunyata Taipan Helix power cord and the combination worked well. The Taipan Helix was, iirc, the third model down in Shunyata's lineup at the time. The PH7 doesn't really need an 8-gauge power cord. You may want to consider whether the PH7 can manifest full benefit from all the features in a cord such as today's Alpha. I wouldn't hesitate to consider the Delta or Venom series with the PH7.
Fwiw, the PH7 definitely benefits from NOS 6DJ8/6922/7308 tube substitution. Say a nice Amperex 6922 circa 1970's.